Chemokines are a family of low molecular weight chemotactic cytokines secreted by cells. Chemokines regulate a broad spectrum of cellular functions and exert their actions by binding to chemokine receptors which are G protein-coupled receptors. Chemokines are divided into different classes based on the positions of the N-terminal cysteine residues within the protein (Charo et al. (2006) N. Engl. J. Med. 354: 610-621). The CXC class of chemokines contains the CXC motif in which the first two cysteines are separated by a non-conserved amino acid. The CXC chemokines may be further divided into the ELR+ and the ELR− subclasses based on the presence or absence of the ELR (glutamic acid-leucine-arginine) motif before the first cysteine of the CXC motif. ELR+ CXC chemokines include interleukin-8 (IL-8; also known as CXCL8), GROα (CXCL1), GROβ (CXCL2), GROγ (CXCL3), neutrophil-activating protein-2 (NAP-2 or CXCL7), epithelial cell-derived neutrophil-activating peptide-78 (ENA-78 or CXCL5) and granulocyte chemotactic protein-2 (GCP-2 or CXCL6). An important function of ELR+ CXC chemokines is to recruit neutrophils to sites of inflammation and induce granule exocytosis and the respiratory burst. All ELR+ CXC chemokines bind to the chemokine receptor CXCR2 (also known as IL-8 receptor β), while IL-8 and GCP-2 bind to CXCR1 (also known as IL-8 receptor α).
CXCR2 is expressed on a variety of cells including neutrophils, keratinocytes, mast cells, eosinophils, macrophages, endothelial cells and neurons including sensory neurons. CXCR2 has been implicated in the pathology of various diseases including inflammatory diseases such as multiple sclerosis, rheumatoid arthritis, psoriasis, chronic obstructive pulmonary disease, inflammatory myopathies and atherosclerosis, neurodegenerative diseases such as Alzheimer's disease and Parkinson's disease, neurodegenerative infectious diseases such as HIV and cancer (Liu et al. (2010) Nat. Neurosci. 13:19-26; Mihara et al. (2005) Eur. J. Immunol. 35: 2573-82; Ono et al. (2003) J. Allergy Clin. Immunol. 111:1185-99; Xia & Hyman (2002) J. Neuroimmunol. 122: 55-64; Edman et al. (2008) Stem Cells 26:1891-1900; Dorsam & Gutkind (2007) Nature Rev. Cancer 7:79-94, Manjavachi et al. (2010), European Journal of Pain, 14: 23-31, Langford et al., J Neurovirol. (2002), 8(6):625-38, De Paepe et al., Acta Neuropathol. (2005), 109(6):576-82.)
Chemotherapy induced peripheral neuropathy (CIPN) is defined as the damage to the peripheral nervous system experienced by patients receiving chemotherapy treatment regimens. CIPN is a prevalent major dose-limiting side effect of many chemotherapeutic agents, including platinum compounds (for example, oxaliplatin), taxanes, vinca alkaloids, thalidomide and newer agents such as bortezomib [Balayssac, Expert Opin. Drug Saf., 10, 407-417, 2011)]. This represents a significant limitation to treatment in many diverse cancers, as end-organ neurotoxicity and neuropathy can require discontinuation of effective therapy with a high impact on a patient's quality of life.
For example, oxaliplatin containing treatment regimens (e.g. 85 mg/m2 every 2 weeks) produce an immediate ‘cold’ sensitive transient paraesthesia and limb muscular spasm in 95% of patients that develops into a symmetric, axonal, sensory distal primary neuropathy without motor involvement [Argyriou, Cancer Treatment Reviews, 43, 368-377 (2008)].
Oxaliplatin uptake and platinum accumulation within the dorsal root ganglion (DRG) and its sensory neurons is a major determinant of the neurotoxicity of oxaliplatin (Jong, J. Pharmacol. Exp. Ther., 338(2):537-47 (2011). In addition, inflammatory cascade activation plays a role in the initiation and progression of CIPN with immune cell infiltration into the injured neuronal environment [Wang, Cytokine, 59, 3-9 (2012)].
The pro-inflammatory chemokine receptor CXCR2 is expressed in sensory neurons and its ligands have been implicated in regulating increases in sodium and potassium currents that govern neuronal excitability [Wang, Mol. Pain, 24, 38 (2008); Yang, Mol. Pain, 5, 26 (2009)]. In peripheral neuronal injuries, the recruitment of CXCR2+ pro-inflammatory secreting immune cells is also known to be involved in both acute and persistent pain and blocked by CXCR2 antagonism [Manjavachi, Eur. J. Pain, 14, 23-31 (2010); Kiguchi, J. Pharmacol. Exp. Ther., 340, 577-587 (2012); Stadtmann & Zarbock, Front. Immunol., 3, 263 (2012)]. CXCR2 ligands have been shown to regulate the function of TRPv1 channels [Dong, Neurosci. Bull., 28, 155-164 (2012)] involved in nociceptive processing and stimulate calcium influx and release of the pain mediating peptide calcitonin gene-related peptide (CGRP) in sensory neurons (Qin, J. Neurosci. Res., 82, 51-62 (2005). Human peripheral nerve explants and Schwann cell cultures express [Ozaki, NeuroReport, 19, 31-35 (2008)] and secrete CXCR2 pro-inflammatory cytokines like IL-8 [Rutkowski, J. Neuroimmunol., 101, 47-60 (1999)] which is significantly elevated in diabetic and alcoholic neuropathies and in length dependent small fiber neuropathy [AboElAsar, Cytokine, 59, 86-93 (2012)]; (Michalowska-Wender, Folia Neuropathol., 45, 78-81 (2007); Üçeyler, Neurology, 74, 1806 (2010)]. The neuronal CXCR2 receptor system has also been shown to regulate re-myelination [Veenstra & Ransohoff, J. Neuroimmunol., 246, 1-9 (2012)] and synaptic plasticity (Xiong, J. Neurosci. Res., 71, 600-607 (2003) processes that govern neuronal communication.
The CXCR2 receptor and its ligands are also upregulated in colorectal cancer and have been implicated in chemoresistance [Acharyya, Cell, 150, 165-178 (2012)], tumor growth, vessel formation, cancer cell proliferation and neutrophil recruitment to the tumor microenvironment [Verbeke, Cytokine & Growth Factor Review, 22, 345-358 (2012)].
In light of the role that CXCR2 plays in the pathogenesis of various diseases, it is desirable to prepare compounds that inhibit CXCR2 activity, which may be used in the treatment or prevention of diseases mediated by CXCR2.